RELATIONSHIP OF MICROSCOPIC AND MACROSCOPIC VEGETATIVE REACTIONS IN RHIZOCTONIA-SOLANI AND THE OCCURRENCE OF VEGETATIVELY COMPATIBLE POPULATIONS (VCPS) IN AG-8

An examination of microscopic and macroscopic vegetative reactions bet ween paired isolated of Rhizoctonia solami AG-8 revealed that pairs of isolates that give a C2 anastomosis reaction at the microscopic level always gives a 'tuft' reaction at the macroscopic level. Similarly, a ny pair that gives a C3 anastomosis reaction at the microscopic level always gives a 'merge' reaction at the macroscopic level. Thus, macros copic vegetative ('tuft type') reactions can be used to predict the mi croscopic (anastomosis) reaction (and vice versa) between paired isola te of AG-8. This pattern also seems to apply to paired isolates of AG- 3, AG-7 and AG-10 but not the other AGs of R. solani. The C2 anastomos is reaction is always observed when two isolates from different zymogr am groups of R. solani AG-8 are paired. When isolates from within any of the five zymogram groups comprising AG-8 are paired, either a C2 or a C3 anastomosis reaction will result. Many field isolates of AG-8, w hen paired, give a C3 anastomosis reaction. We propose that a group of field isolates of R. solani that give a C3 anastomosis reaction be de signated a 'vegetatively compatible population' (VCP).